Contraries become strictly incompatible only when subject, time, and relevant respect are the same. Someone may be seated and then standing; the two states occur in succession rather than at once.
A student may pass one subject while failing another. Although “pass” and “fail” oppose each other linguistically, there is no contradiction because they refer to different assessments.
Before declaring a proposition intrinsically impossible, determine whether the affirmation and negation apply to precisely the same thing in the same respect.